Disc brake caliper

ABSTRACT

A disc brake caliper including a brake piston movably arranged therein. The brake piston is sealed in relation to the brake cylinder by a sealing ring, which is arranged in a circumferential annular groove of the brake cylinder. The sealing ring functions to retract the brake piston in the brake cylinder after a braking operation in order to provide a clearance between a brake shoe and a brake disc. According to the present invention, the annular groove includes a recess, which is arranged in the area of transition between a groove wall and the cylinder surface . The contour line, which defines the cross-section of the recess, starting from the groove wall of the annular groove, passes from a convexly curved portion over into a concavely curved portion. This permits ensuring an unchangingly constant clearance between the brake shoe and the brake disc roughly irrespective of the hydraulic pressure.

TECHNICAL FIELD

The present invention relates to a disc brake caliper and moreparticularly relates to sealing rings used in disc brake calipers.

BACKGROUND OF THE INVENTION

A generic disc brake caliper is disclosed in German patent applicationNo. 42 02 927. The prior art disc brake caliper includes a hydraulicactuating device, which is comprised of an open brake cylinder and abrake piston, which axially slidably arranged in the brake cylinder. Thebrake piston and the brake cylinder are sealed in relation to each otherby means of a sealing ring, which is mounted in a circumferentialannular groove in the inside of the brake cylinder and is in frictionalabutment on an external peripheral surface of the brake piston forsealing purposes. The purpose of the sealing ring not only is to sealthe interior of the brake cylinder. The sealing ring, due to its elasticproperties, additionally assists in adjusting a clearance between thefriction surfaces of the brake shoes and the brake disc after the brakeapplication.

Upon brake application, hydraulic pressure is applied to the brakepiston and causes it to move out of the brake cylinder in an axialdirection. Upon axial displacement of the brake piston, the sealingring, which bears against the external peripheral surface of the brakepiston, is deformed elastically due to the friction (in first line:static friction) between the sealing ring and the brake piston. Upontermination of the brake application, i.e., when the hydraulic brakesystem is relieved from load, the elastic sealing ring will return toits original shape and shift the brake piston by a small amount into thebrake cylinder. A brake shoe, which abuts the brake piston, follows theaxial displacement of the brake piston, and its friction surface islifted from the brake disc so that a clearance is maintained between thebrake shoe and the brake disc.

The amount of the adjusted clearance generally depends on thecharacteristics of the sealing ring and the annular groove accommodatingthe sealing ring, especially the cross-sectional shape of the annulargroove. Another undesirable relationship is associated with thehydraulic pressure, which prevails in the brake cylinder during brakeapplication: The higher the hydraulic pressure, the more the sealingring deforms. Attempts have generally been made to maintain anunchanging constant clearance after each brake application irrespectiveof the hydraulic pressure that occurs. To achieve this objective, aplurality of various cross-sectional shapes for the annular groove havebeen proposed so far. However, none of the cross-sectional shapespermitted achieving a fixed clearance irrespective of the hydraulicpressure.

For example, in the disc brake caliper disclosed in German patentapplication No. 42 02 927, a transition area, which is defined byadjacent circumferential conical surfaces or torus surfaces, is providedbetween the annular groove wall and the cylinder surface. The sealingring is urged, at least in part, into this transition area during brakeapplication. However, this embodiment does not either ensure apressure-independent clearance. Further, damage to the sealing ring maybe caused, especially when high hydraulic pressures are applied, becausethe sealing ring will yield far into the acutely tapering transitionarea in this case. This will greatly reduce the useful life of a sealingring of this type.

An object of the present invention is to improve a generic disc brakecaliper with respect to its clearance. The special objective is toachieve a fixed clearance irrespective of the hydraulic pressureapplied.

This object is achieved by the present invention by fashioning acircumferential recess in the transition area between the brake cylindersurface and the groove wall of the annular groove, which is orientedsubstantially vertically to the brake piston axis. The recess is definedin its cross-section by a contour line, which starts from the groovewall in a convex curvature and passes over into a concave curvature.Depending on the hydraulic pressure applied, a corresponding elasticdeformation of the sealing ring into the circumferential recess ispermitted. The circumferential recess is in first line arranged at thatgroove wall of the annular groove, which is closest to the open end ofthe brake cylinder.

To minimize damages to the material of the elastic sealing ring, thesectionwise different radii of curvature of the contour line of thecross-section of the recess will continuously pass into one another in apreferred embodiment of the disc brake caliper. The fabrication of therecess may be simplified by defining the recess at least in sections bycircumferential conical partial surfaces.

In a preferred aspect of the cross-section of the recess, the contourline and the brake cylinder surface form a preferably right angle. Thisreduces symptoms of wear on the sealing ring, especially at highhydraulic pressures.

Another preferred aspect of the cross-section of the recess is obtainedby providing a radial elevation in the contour line so that the freespace available for the elastic deformation of the sealing ring iscontracted. This avoids an excessive deformation of the sealing ringinto the recess at medium hydraulic pressures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional diagrammatic sketch of a disc brake caliperaccording to the present invention.

FIG. 2 an enlarged view of detail A in FIG. 1.

FIG. 3 is an enlarged cross-sectional view of an annular groove with arecess.

FIGS. 4, 5, 6 and 7 are enlarged cross-sectional views of differentembodiments of the recess at the annular groove.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The disc brake caliper 1 illustrated in FIG. 1 straddles the outsideedge of a brake disc 2, as well as brake shoes 3, 4 arranged on eitherside of the brake disc 2. The disc brake caliper 1 includes an axiallyinward leg 5 and an axially outward leg 6, against, which the axiallyouter brake shoe 3 is directly bearing. The inward caliper leg 5 has ahydraulic actuating device 7 which is comprised of a brake cylinder 8and a brake piston 9. The brake piston 9 is axially slidable in thebrake cylinder 8. With its end projecting from the open brake cylinder8, the brake piston 9 abuts on the axially inner brake shoe 4. Brakepiston 9 is sealed in relation to the brake cylinder 8 by means of anelastic sealing ring 10. The sealing ring 10 is accommodated in acircumferential annular groove 11 in the inside of the brake cylinder 8.Groove 11 is indented into the cylinder surface 12 of the brake cylinder8. The annular groove 11 is generally comprised of a groove bottom 13,which extends transversely to the cylinder surface 12, and two groovewalls 14, 15, which are oriented substantially vertically to the brakecylinder axis. Apart from providing hydraulic sealing, the sealing ring10 still has the function of retracting the brake piston 9 along withthe brake shoe 4 connected thereto, if possible to its initial position,upon termination of brake application and, thus, reduction of thehydraulic pressure. This adjusts a clearance between the brake shoe 4and the brake disc 2. To this end, the annular groove 11 is providedwith a circumferential recess 16 in its transition area between thecylinder surface 12 and the groove wall 14. When the brake is applied,the sealing ring 10, which is in frictional abutment on the brake piston9 is entrained by the axially displacing brake piston 9 and thus yieldselastically into the recess 16.

The embodiment of FIG. 3 shows an enlarged cross-sectional view of theannular groove 11 with the adjacent recess 16. It can be seen that thecontour line 17, which defines the cross-section of the recess, startingfrom the groove wall 14, commences with a convexly curved portion 18 andpasses into a concavely curved portion 19. The circumferential recess 16is arranged at that groove wall 14 of the annular groove 11, which isclosest to the open end of the brake cylinder 8. When the brake isapplied at low hydraulic pressure, the sealing ring 10, due to theconvex curvature 18, yields elastically into the recess 16 only to asmall extent. In addition, the recess 16 still has sufficient space inthe area of the concavely curved portion 19 of the contour line 17,which is provided to accommodate the elastic deformation of the sealingring 10 when exposed to high hydraulic pressure. This achieves thepossibility of adjusting an unchangingly constant clearance, which isroughly irrespective of pressure.

FIGS. 4 to 7 show enlarged views of different embodiments ofcircumferential recesses 16 at the annular groove 11, which aredifferent regarding the course of the contour line 17 defining thecross-section of the recess. Seen in FIG. 4 can be seen a roughlyS-shaped course of the contour line 17 which is produced when thecontour line 17, starting from the groove wall 14, passes from aconvexly curved portion 18 into a concavely curved portion 19. Thesectionwise different radii of curvature of the contour line 17 havetangential transitions, whereby material wear on the sealing ring 11 isreduced. When the brake is applied at low hydraulic pressure, thesealing ring 11 will yield only partly into the recess 16, roughly inthe area, which is defined by the convexly curved portion 18. Only atvery high hydraulic pressure in the brake system will the elasticsealing ring 11 yield into the entire cross-section of the recess 16,when the brake is applied, until its elastic deformation comes to a stopby abutment on a stop surface 20. The stop surface 20, which, preferablyin all embodiments of the recess 16, is at a right angle (which ispreferred) to the cylinder surface 12 in the direct area of transitionto the brake cylinder, limits the elastic deformation of the sealingring 11 in an axial direction. This prevents above all an excessive wearof material on the sealing ring 11. With a reduction of hydraulicpressure in the brake system, the sealing ring 11 will deform axiallyinto its initial position (provided a material with appropriate elasticproperties has been chosen) and entrains the brake piston 9 byfrictional abutment on its peripheral surface. This general mode ofoperation may also be transferred to the variations of FIGS. 5 to 7,which have a different configuration. In FIG. 5, the area of the contourline 17, which is adjacent to, the groove wall 14 of the annular groove11 has straight portions 21 for reasons of simplification ofmanufacture. The contour line 17 is at least partly comprised ofportions of a simple geometric outline, such as a straight line, andthus permits favorably manufacturing the recess by way of machiningoperations. In particular, the straight portion 21, which is directlyadjacent to the groove wall 14 and has a slight angle relative to, thegroove wall has the special purpose of providing a stop surface 22 forthe sealing ring 10 when low pressure prevails in the brake system. Insuch a case of operation, the sealing ring 10 is deformed elastically tocontact the abutment surface 22 and, extending further into theinterspace until it comes into contact with the peripheral surface 23 ofthe brake piston (see dash-and-dot line in FIGS. 4 to 7), yields only toa slight extent into the recess 16 as is shown by the sealing ringcontour 24 in FIGS. 5 to 7. Only at a considerably higher hydraulicpressure will the recess 16 be filled to a greater degree by theelastically deformed sealing ring 10. This provides the possibility ofadjustment of an unchangingly constant clearance over a very widepressure range.

The variations shown in FIGS. 6 to 7 illustrate another approach ofachieving a constant clearance, which is irrespective of pressure. Thecontour line 17, which defines the cross-section of the recess 16,includes a radial elevation 25 on its right-hand side close to theannular groove 11 in FIGS. 6 and 7. The free distance between thecontour line 17 and the peripheral surface 23 of the brake piston iscontracted by this radial elevation 25. This produces an obstacle forthe sealing ring 10, which yields elastically into the recess 16,especially when the brake is applied at medium hydraulic pressure. Onlywith further pressure rise will the sealing ring 10 be in a position toovercome the contraction between the contour line 17 and the peripheralsurface 23 of the brake piston and to fill the left-hand area of therecess 16 (see FIGS. 6 and 7), which lies axially behind thecontraction. The unchangingly constant clearance can be adjusted by thisprovision over a wider range of hydraulic pressure.

The manufacture is additionally simplified also for the variationsaccording to FIGS. 6 and 7 by composing the contour line 17 at least inpart of straight portions 21. This becomes apparent especially in FIG. 7in the connecting portion between the convexly curved portion 18 and theconcavely curved portion 19.

What is claimed is:
 1. Disc brake caliper comprising: a hydraulicactuating device which includes a brake cylinder with an open end, abrake piston, which is axially movably arranged therein, the actuatingdevice having an elastic sealing mounted in a circumferential annulargroove in the inside of the brake cylinder and being in frictionalabutment for sealing an external peripheral surface of the brake piston,wherein said circumferential annular groove includes groove walls, andwherein at least one of the groove walls of the annular groove includesa circumferential recess in the area of transition between the cylindersurface of the brake cylinder and the groove wall of the annular groove,into which recess the sealing ring is urged elastically by the brakepiston, which is moved in an axial direction when the brake is applied,wherein the circumferential recess is arranged at the groove wall of theannular groove that is closest to the open end of the brake cylinder,and in its cross-section is defined by a contour line, which, startingfrom the groove wall of the annular groove adjacent to the recess at aright angle between the contour line and the cylinder surface, passesfrom a convex curvature over into a concave curvature, and thesectionwise different radii of curvature of the contour line of thecross-section of recess tangentially pass into one another.
 2. Discbrake caliper as claimed in claim 1, wherein the contour line, at leastin part, has straight portions.
 3. Disc brake caliper as claimed inclaim 1, wherein the contour line which defines the cross-section of therecess includes a radial elevation so that the free space between thecontour line and the peripheral surface of the brake piston iscontracted.